Resource Pack See-Through Items

What I expected to happen was...:
I expected my resource pack to display items normally, as it does when I use any Minecraft version that was released before 1.8.

What actually happened was...:
When using any version 1.8+, certain item textures are see-through from the side while using a resource pack; such as the sword texture.

Steps to Reproduce:
1. Get a resource pack
2. Use resource pack in-game
3. Voilà, certain item textures are see-through from the side